In ecstasy tablet, rat poison extremely reckless (6)
I believe the answer is:
enrapt
'in ecstasy' is the definition.
(I've seen this before)
'tablet rat poison extremely reckless' is the wordplay.
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'extremely' suggests removing the centre (only the extremes of the word are used).
'reckless' indicates anagramming the letters.
'poison' with its centre removed is 'pn'.
'rat'+'pn'='ratpn'
'ratpn' anagrammed gives 'nrapt'.
'e'+'nrapt'='ENRAPT'
(Other definitions for enrapt that I've seen before include "state of ecstasy" , "Fascinated" , "Turned on" , "Deeply absorbed in something" , "Sent" .)